Thanks, @agrant! These all ranged in period of time worked on. The Law of Sine/Cosine calculator took a couple of months while the ones at the top were a couple of days.
A great rule of thumb that helped last year during the pilot turned out to center around supporting the students' interests anyway! If I noticed a student working on something that seemed bigger than one lesson, I would make a quick link (using bit.ly or tinyurl) directly to that project and have it ready somewhere. Then, each day when that student finished early, I gave him/her the link to the project and they spent a few minutes working on it. In that way, it sometimes did take weeks.
Some really great ideas will come out of your kiddos during those lessons so keep an eye out!